1. Field of the Invention
The present invention relates to a heating apparatus performing a heating process on a substrate coated with a coating liquid, a coating and development apparatus including the heating apparatus, and a heating method.
2. Description of the Background Art
An apparatus for forming a resist pattern on a glass plate for a semiconductor wafer (referred to as a wafer hereinafter) and an LCD (Liquid Crystal Display) includes a coating and development apparatus applying a resist on a wafer and developing the exposed wafer. This apparatus is equipped with a heating apparatus called a baking apparatus or the like. An apparatus that heats a wafer coated with a resist liquid, for example, serves to dry a solvent in the resist liquid.
Such a heating apparatus generally includes a hot plate 11, over which a cover body 12 lies, as shown in FIG. 13. While gas is supplied to the inside of cover body 12 from a gas supply port 13 formed around the entire circumference of a wafer W1, the gas is sucked and exhausted from the central portion of the cover body 12. In this manner, a heating process is performed while a gas flow from the outer circumference of the wafer toward the center is formed, as represented by the arrow in the figure. However, when a gas flow is formed in this manner, sublimation substances subliming from the resist liquid is likely to attach to the wafer as particles even with a uniform temperature within the surface of hot plate 11, for which reason is not clarified, though.
On the other hand, Japanese Patent Laying-Open No. 2004-293924 discloses a heating apparatus performing dry processing on a glass substrate for LCD coated with a polyimide solution for an alignment film, in which a passage of a gas flow is formed by placing a cover over a region above a hot plate. A heating process is performed while a gas flow from an opening on one side of the passage toward the other side is formed. The inventor understands that the amount of the attached sublimation substances on the wafer is reduced when the technique of forming a gas flow from one end side to the other end side, so to speak, a unidirectional flow is applied to the wafer heating apparatus, as compared with when a gas flow is formed from the outer circumference to the center of the wafer. In this case, however, the velocity of flow is high at the other end side of a wafer from which a gas flow is exhausted. Therefore, the heating process may not be uniform, so that the resist film may lack uniformity.
In addition, such a heating apparatus has also the following problem. The particles on the heating plate is transferred to the wafer when the wafer is brought into surface contact with the heating plate. Thus, a plurality of protrusion portions each having a height of 0.1 mm are usually provided on the heating plate, so that the wafer placed thereon is slightly isolated from the heating surface (Japanese Patent Laying-Open No. 2001-274052). This height is set at a minimum value such that the wafer does not contact with the heating surface. With a larger value, it is difficult to keep the wafer-heating temperature uniform.
Now, with the increased wafer size in diameter, a semiconductor manufacturing apparatus for a 12-inch wafer (a diameter of 30 mm) is put into practice, and a wafer with a even larger diameter has been developed. However, with the 12-inch or larger size, some wafers may badly warp. Accordingly, with a height of 0.1 mm of a protrusion provided on the heating plate, the wafer may come into contact with the hot plate and become misaligned. Moreover, when the wafer is delivered onto the hot plate (the protrusion portion), the wafer may slide sideways as if it is placed on an ice face. This phenomena takes place since an air layer is presumably formed in such a manner that the air is enclosed and slightly pressurized in a small space under a large-diameter wafer.